Radio frequency identification (RFID) is a technology that works on radio frequency signals. An RFID system often comprises three main components: (1) an RFID tag which stores data is usually attached to an article that one desires to identify and/or track; (2) an RFID reader that communicates with the RFID tag using radio frequency signals to obtain data from the RFID tag; and (3) a host data processor that uses the data obtained by the RFID reader from the RFID tag. If the RFID tag is within range of the radio frequency signals (radio waves), a communication link between the two RFID devices is established and the RFID tag replies with data to the RFID reader. Based on this reply, the RFID reader may identify the article.
There are various types of RFID tags. Passive RFID tags do not include a power source, such as a battery. Passive RFID tags rely on power derived from radio waves from the RFID reader to transmit a reply to the RFID reader. Active RFID tags include a power source to power its internal circuity and to enable transmission of a reply to the RFID reader. Semi-passive RFID tags include a power supply to power its internal circuity but relies on power derived from the radio waves from the RFID reader to transmit a reply to the RFID reader.
An important factor is range, which refers to the maximum distance between the RFID reader and RFID tag for a reliable communication link between the two RFID devices. The range is affected by various factors, such as background radio frequency noise, surrounding structures that may affect the radio waves from the RFID reader, antenna configurations of the reader and tag, relative orientation (angle) between the reader and tag, and carrier frequency. RFID systems may operate in different frequency bands. In the low frequency (LF) band, a carrier frequency of 125 kHz or 134 kHz, for example, may provide a range up to 10 cm. In the high frequency (HF) band, a carrier frequency of 13.58 MHz, for example, may provide a range up to 1 meter. In the ultra high frequency (UHF) band, a carrier frequency within 860-960 MHz, for example, may provide a range up to 15 meters. RFID tags are used on a great variety of articles. The articles can be items of clothing for sale in a retail shop, medical devices, and individual components used in a factory, just to name a few. Sometimes, RFID tags are scanned individually by an RFID reader at a relatively close range. At other times, the same RFID tags may need to be scanned by an RFID reader from far away. In FIG. 1 for example, many articles 100 each having an RFID tag may be grouped together for storage, and it may be desired to scan the RFID tags together as a group. Articles 100 may be stored on a pallet and transported together from a manufacturing facility to retail facility, for example. To track individual articles 100 during transportation, the entire group may be passed across an RFID screening station having one or more RFID readers 102 which are located further away than usual. To enable reliable communication, the RFID tags may be over-designed or conservatively designed to work in the most extreme situation that is expected during the useful life of the RFID tags, but such an approach may increase costs significantly. This scenario and others present a need for RFID tags that can be modified to suit the environment in which they will be scanned.